胰岛素如同打开细胞大门的钥匙

Insulin Acts a Key to Open Up Cell to Receive Glucose

 

　

胰岛素(INSULIN)影响碳水化合物、蛋白质和脂肪代谢。你的身体将这些营养物质分解成糖分子、氨基酸分子和脂质分子。身体也可以储存和重组这些分子，形成更复杂的形式。胰岛素会导致这些营养物质的储存，而另一种叫做胰高血糖素（GLUCAGON））的胰腺激素会释放这些营养物质。

　

 

　

胰岛素与你身体的谨慎平衡有关，使你的血糖水平保持在正常范围内。简而言之:

如果你的血糖过高:胰腺释放胰岛素，帮助细胞从血液中吸收葡萄糖，从而降低血糖水平。

如果你的血糖很低:胰腺释放胰高血糖素，帮助肝脏释放储存在肝脏中的葡萄糖，从而提高血糖水平。

　

　

 

当大多数食物被消耗时，血糖水平会升高，但是随着碳水化合物的摄入，血糖水平会升高得更快更剧烈。消化系统从食物中释放葡萄糖，葡萄糖分子被血液吸收。上升的葡萄糖水平表明胰腺分泌胰岛素以清除血液中的葡萄糖。胰岛素与细胞表面的胰岛素受体结合，作为打开细胞大门让葡萄糖进入的钥匙。

　

　

 

几乎所有的组织都有胰岛素受体，包括肌肉细胞和脂肪细胞。

 

胰岛素受体有两个主要的组成部分——外部和内部部分。外部部分延伸到细胞外并与胰岛素结合。当这种情况发生时，受体的内部部分会在细胞内发出信号，让葡萄糖转运体运动到表面并接收葡萄糖。当血糖和胰岛素水平降低时，受体就会空出来，葡萄糖转运体就会回到细胞中。

　

　

 

 

How Insulin Works

Insulin affects carbohydrate, protein, and fat metabolism. Your body breaks these nutrients down into sugar molecules, amino acid molecules, and lipid molecules. The body can also store and reassemble these molecules into more complex forms. Insulin causes the storage of these nutrients, while another pancreatic hormone called glucagon releases them from storage.

 

Insulin is involved in your body's careful balancing act to keep your blood sugar levels within a normal range. In simple terms:

 

 

If your blood sugar is high: The pancreas releases insulin to help cells absorb glucose from the bloodstream to lower blood sugar levels.

If your blood sugar is low: The pancreas releases glucagon to help the liver release stored glucose into the bloodstream to raise blood sugar levels.

 

Blood sugar levels rise when most foods are consumed, but they rise more rapidly and drastically with carbohydrates. The digestive system releases glucose from foods and the glucose molecules are absorbed into the bloodstream. The rising glucose levels signal the pancreas to secrete insulin to clear out glucose from the bloodstream. Insulin binds with insulin receptors on cell surfaces and acts as a key to open up the cells to receive glucose. Insulin receptors are on almost all tissues, including muscle cells and fat cells.

 

 

Insulin receptors have two main components—the exterior and interior portions. The exterior portion extends outside the cell and binds with insulin. When this happens, the interior part of the receptor sends out a signal inside the cell for glucose transporters to mobilize to the surface and receive glucose. As blood sugar and insulin levels decrease, the receptors empty and the glucose transporters go back into the cell.

 

How Insulin Works in the Body  https://www.verywellhealth.com/how-insulin-works-in-the-body-1087716

　

　

The Regeneration of Beta Cells

　

 A study, conducted at the University of Geneva and co-funded by the Juvenile Diabetes Research Foundation, has found that alpha cells in the pancreas, the cells which secrete the hormone glucagon, can regenerate themselves into insulin-producing beta cells after normal beta cells have been destroyed. The study is the first to show that this change of alpha cell into beta cell can happen naturally and spontaneously.

The researchers, led by Dr. Pedro L. Herrera, discovered that when they destroyed beta cells in mice to induce an artificial form of type 1 diabetes, the alpha cells in the pancreas then changed into insulin-producers. They found that when nearly all of the beta cells had been destroyed, if mice were given insulin therapy to keep them alive, the alpha cells spontaneously changed into functioning beta cells. After enough alpha cells converted into beta cells, insulin therapy was no longer needed. The Geneva researchers pointed out that the critical factor in sparking the alpha-to- beta-cell reprogramming was removing (or ablating) nearly all the original insulin-producing cells in the mice. In mice where the loss of beta cells was more modest, the researchers either found no evidence of beta cell regeneration (when only half the cells were destroyed) or less alpha cell reprogramming (when less than 95% of cells were destroyed).

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It has been previously shown that alpha cells can be converted into beta cells, but this work relied on genetic manipulations – forcing expression of a key beta cell transcription factor, Pax4, in alpha cells. What is new in Dr. Herrera’s work is the demonstration that the ability of alpha cells to convert to beta cells appears to be intrinsic and can occur without genetic manipulation of the cells. We know a bit about some of the transcriptional changes that accompany the conversion of alpha cells to beta cells, but we still do not know the signals that trigger those changes. One of the current challenges is to identify the signals and pathways that are triggering the reprogramming of alpha cells to beta cells and ways to manipulate those pathways.

Many different studies have shown that we can make insulin producing cells. Do you believe that this is different and if so, how?

Being a beta cell is more than just producing insulin. Beta cells must be able to continuously sense the level of glucose and secrete insulin appropriately in response to the body’s needs. What is exciting about these results is the demonstration that the body can spontaneously make new beta cells from pre-existing alpha cells and that these new beta cells are functional and able to control glucose levels. The demonstration that the conversion of alpha cells to beta cells is a spontaneous and normal process raises hope that we can identify therapeutic interventions that will mimic this process to safely and efficiently reprogram alpha cells to beta cells for the treatment of diabetes.

There is research that shows the cells that line the ducts of the pancreas can convert to beta cells. Do you think these findings contradict or support the idea that beta cells might come from ducts?

These findings don’t rule out a ductal or duct-associated beta cell progenitor. One of the emerging themes coming from this work and other work is that the pancreas is more plastic than we previously appreciated – there appear to be multiple mechanisms and sources for beta cell regeneration.

https://asweetlife.org/the-regeneration-of-beta-cells/